IT/Tech Due Diligence

First off, it is fundamental to clarify the situation. 
There is a big difference between an IT DD for a carve out (i.e., separation of a business unit from a larger business), an M&A and then integration of firms, and a PE fund just buying a company to keep it standalone or make it a platform for add-ons.

The first case is arguably the most complex one because you have to understand which IT services are provided by the larger business and which can be available standalone from day one or through agreements with the seller.

In any case, an IT DD has the goal to understand:

1. Map of the systems used by the target
2. Dependency between systems and with other players (outsourcers, sellers, other portfolio companies, etc)
3. System readiness from day 1 after closing
4. Level of digitalization across company functions (i.e., tools used by salesforce or accounting dept)
5. The maturity level of those systems (i.e., Saas vs on-premise, need for upgrades, state-of-the-art development, frequency of updates, glitches/bugs)
6. Total Cost of Ownership of those systems
7. Investments needed to have a cost-effective IT infrastructure (and potential savings)
8. People and IT organization needed to run the show

Good luck with your final round!

How lucky that I've created a case exactly on this topic :) (Based on a real-life company/scenario)

https://www.preplounge.com/en/management-consulting-cases/candidate-led-usual-style/intermediate/roma-solutions-senior-expert-level-tech-case-240

I stongly doubt that you're going to get an IT DD as a case. But it doesn't hurt to have a look. I think the materials already provided should suffice.